Why is this weird line in appearing in Glass material?
It just occurred to me that this is probably a case of reversed normals seeing as the entire shading of the coffee is off. A Normal is a line that comes off perpendicular to a plane. Blender uses these to calculate lighting off the various faces of a mesh, but if they're facing the wrong way (inside rather than outside), then the shading of the object will not look right.

To check if the normals are facing the correct direction, open the Viewport Overlays drop-down menu, and check Face Orientation. If the normals are facing the right way (as in facing in the direction the object is meant to be viewed), than the object will appear blue. If not, it will be red.



If this is the case, Tab into edit mode with the coffee selected, and press Shift+N to recalculate normals.